In a power tool such as a hammer and a hammer drill, during hammering operation or hammer drill operation by a hammer bit, the hammer bit is acted upon by a reaction (hereinafter referred to as a reaction force) from a workpiece. At this time, the hammer bit is caused to move by the reaction force not only in an axial direction of the hammer bit (fore-and-aft direction), but also in vertical and lateral directions transverse to the axial direction, and this motion is transmitted to a tool body via a tool holder which holds the hammer bit. Generally, in a power tool in which vibration is caused during operation, a mechanism for reducing transmission of vibration to the user is devised. For example, transmission of vibration caused in the tool body to the handgrip is reduced or prevented by connecting a handgrip to be held by a user to the tool body via an elastic element. One example is disclosed in Japanese Patent Publication No. 58-34271.
However, the above-described known vibration-proofing mechanism is constructed to prevent transmission of vibration to the handgrip to be held by a user. Therefore, it is difficult to prevent an external force which is caused by irregular motion or run-out of the hammer bit when the hammer bit is acted upon by a reaction force from a workpiece, from being transmitted to the tool body.